Prosthetic heart valve with improved blood flow

ABSTRACT

A prosthetic heart valve is shown which incorporates a valve body design and leaflet pivot arrangements that minimize turbulence and shear stresses having a tendency to generate thrombosis. A valve body having an axially curved entrance that is smoothly joined to a generally cylindrical body of extended axial length provides excellent fluid flow characteristics when combined with leaflets that can assume orientations perfectly aligned with the downstream flow of blood. By constructing such a pyrocarbon valve body which receives a metal ring at an appropriate location, suture rings that permit the tissue annulus to directly contact the exterior surface of the cylindrical valve body are accommodated.

BACKGROUND OF THE INVENTION

The present invention relates to heart valve prostheses, and inparticular to mechanical heart valves having occluders that pivot andtranslate in moving between open and closed orientations.

DESCRIPTION OF THE PRIOR ART

Various types of heart valve prostheses have been developed whichoperate hemodynamically as a result of the pumping action of the heart.In the last decade, the bileaflet heart valve has generally become themechanical valve of choice; however, some single occluder valves arestill being offered. More recently, attention has also begun to be givento trileaflet valves. The study of blood flow through such multipleleaflet valves has convinced many investigators that it is veryimportant that emphasis should be given to achieving designs withminimum turbulence and minimum pressure drop. It was generally believedthat the shorter the axial length of a valve body was, the less would bethe resistance to blood flow through the critical region of the valve,because the valve body was of course the region of greatestconstriction. Many patented valve designs also concentrated on the shapeand the placement of the occluders to minimize pressure drop andturbulence.

A number of U.S. patents, such as U.S. Pat. Nos. 4,363,142, 4,328,592,5,178,632 and 5,171,623 illustrate heart valves having relatively shortvalve bodies of generally circular cross-section, some of which haverounded or radially outwardly flared upstream and downstream ends. U.S.Pat. No. 5,078,739 shows a heart valve having a sloping entrance endwherein the leaflets are mounted external of the valve body viaresilient hinges embedded in the downstream end surface of the valvebody. U.S. Pat. No. 4,775,378 shows a heart valve having a singleoccluder with a shallow S-shaped curvature that is alleged to promotethe formation of a stable closed vortex on the suction side of theoccluder; it is employed in combination with a valve body having acircular cross-section passageway that is continuously and increasinglyconstricted, i.e. its diameter decreasing, in the downstream direction.U.S. Pat. No. 4,846,830 discloses a bileaflet valve having a similarvalve body wherein a pair of curved leaflets are employed which arearranged to create a venturi tube nozzle in the direction of downstreamflow which is alleged to avoid vortex formation. U.S. Pat. No. 4,995,881shows a valve having a similarly sloping entrance in combination with apair of leaflets that are curved in the downstream direction so as todefine a nozzle-shaped passage centrally between the two leaflets whenthey are in their open position orientation.

The more that such mechanical prosthetic valves have been studied, themore that investigators have concluded that the ideal prosthetic valvesimply does not yet exist. From a materials standpoint, pyrolytic carbonhas been determined to be adequately nonthrombogenic; as a result, theproblem of combatting thrombosis in mechanical valves is presently feltto lie in preventing excess turbulence, high shear stresses and localregions of stasis. Blood is a very delicate tissue, and even minorabuses caused by turbulence and high shear stress can cause eitherthrombosis or emboli generation at local regions of stagnation.Therefore, it is felt that future improvement in the characteristic ofthromboresistance in mechanical valves will likely be attained throughthe achievement of smooth, nonturbulent flow and the absence of stasis.Accordingly, the search for mechanical valves having such desirablecharacteristics has continued.

SUMMARY OF THE INVENTION

It has now been found that sources of turbulence in mechanical heartvalves that can damage blood and lead to clotting are found to existboth at the leading edges of leaflets that are inclined to the directionof blood flow and at the leading edge of the valve body orifice itself.When a liquid must pass around a corner, as when entering an orifice,separation occurs, and turbulence and elevated shear stresses arecreated in such zone of separation. It has now been found that, byselecting a valve body of relatively extended axial length, by mountingleaflets therein so that, in their open orientation, the leaflets areindividually free to generally follow blood flow and orient themselvesso as to be parallel to the direction of downstream blood flow at anyinstant (to minimize the turbulence associated with the leaflets), andby also contouring the orifice inlet to eliminate that usual zone ofseparation that would otherwise be present, both head or pressure lossand the tendency for thrombosis generation are concomitantly decreased.

More specifically, it has been found that the entrance at the upstreamend of the valve body should be essentially a section of a torus havinga radius of curvature which is at least about 28% of the radius of thecentral passageway through the valve body and not greater than about80%, that the valve body should have an average axial length at leastabout equal to the central passageway radius, and that the flaringtoroidal entrance section should encompass essentially 360° of thecircumference of the opening and extend for an axial distance notgreater than about one-third of the average axial length of the valvebody. Preferably the surface is at least about 30% of a quadrant of atorus which at its downstream end is preferably tangent to the remainderof the interior surface which is preferably generally cylindrical.Because the flow through such a valve body has been found to be afunction of the fourth power of its diameter, the diameter of thepassageway through such a valve body is maximized by using the thinnestvalve body wall that is structurally adequate, in addition having theaverage axial length of the valve body be equal to at least about theradius of the interior cross-section. It has been found that theinterior diameter can be advantageously maximized by allowing theexterior surface of the valve body to interface directly with the tissueannulus from which the natural valve has been excised. Accordingly,suture rings are employed which permit both mitral valves and aorticvalves to be so located that the raw tissue annulus interfaces directlywith the pyrocarbon outer surface of the valve body. The mitral valvesuture ring may be a fairly straightforward design; however, for areplacement aortic valve, a suture ring is designed to permit the valveto be located above the aortic annulus in a location so that itsupstream flared entrance will be slipped into the aortic orifice regionso that its outer wall surface interfaces directly with the tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bileaflet heart valve embodyingvarious features of the present invention with the leaflets shown in theopen position.

FIG. 2 is a sectional view taken generally along the line 2--2 of FIG. 1showing the heart valve with the leaflets in the full open position,upon which a suture ring is installed that is designed to permit thevalve to be mounted in the aortic position.

FIG. 2A is a sectional view taken generally along the line 2--2 of FIG.1 showing the leaflets in the full open position, and with analternative suture ring attached to the valve body.

FIG. 3 is a view similar to FIG. 2 showing the leaflets in theirprerotation orientation as they would be when the downstream flow ofblood slows prior to reversal.

FIG. 3A is a fragmentary sectional view taken along the lines 3A--3A ofFIG. 3.

FIG. 4 is a view similar to FIG. 2, showing the leaflets in elevationand in their closed position, with the suture ring omitted.

FIG. 5 is a plan view looking downward at the valve shown in FIGS. 1 and2 with the leaflets in the full open position.

FIG. 6 is a vertical sectional view through the valve taken generallyalong the line 6--6 of FIG. 2 with the leaflet in the full openposition.

FIG. 7 is a perspective view of a leaflet from the valve of FIG. 1.

FIG. 8 is a side elevation view, reduced in size, of the leaflet of FIG.7.

FIG. 9 is a front view of the leaflet of FIG. 8.

FIG. 10 is a fragmentary sectional view, enlarged in size, taken alongthe line 10--10 of FIGS. 5 and 6 with the sewing ring removed, whichillustrates the freedom of the leaflet in question to rotate clockwisein the open position to assume an orientation of least resistance todownstream blood flow through the valve.

FIG. 10A is a full sectional view similar to FIG. 10 with the right-handleaflet omitted and with the left-hand leaflet shown in the prerotationposition.

FIGS. 11 and 12 are fragmentary horizontal sectional views takenrespectively along the lines 11--11 and 12--12 of FIG. 3, with theleaflets removed.

FIG. 13 is a fragmentary sectional view taken generally along the line13--13 of FIG. 2A.

FIG. 14 is a fragmentary sectional view, enlarged in size, illustratingthe valve body wall structure.

FIG. 15 is a view similar to FIG. 14 showing the aortic sewing ringattached.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Illustrated in FIG. 1 is a preferred embodiment of a prosthetic heartvalve 11 constructed so as to embody various features of the presentinvention. Very generally, heart valves having this construction haveimproved flow characteristics, particularly when the valve is in itsfully open position, because the occluders can align parallel to thevalve centerline or can align at slight deviations thereto dependingupon instantaneous local variations in the blood flow path through thevalve. As a result, such potential occluder or leaflet orientationsminimize turbulence at the upstream edge surfaces thereof andsubstantially reduce drag and boundary layer separation along theirmajor surfaces. This valve design also provides good washingcharacteristics which prevents stagnation and potential clotting.Importantly, heart valves of this design can incorporate pivotarrangements which exhibit a rapid response to change in the directionof blood flow, i.e. in initiating both opening and closing, and whichreduce hemolysis or similar injury to blood cells because of the mannerin which the occluders close against the valve body.

Heart valve 11 includes a generally annular valve body 13 that supportsa pair of pivoting occluders or leaflets 15 which open to allow the flowof blood in the downstream direction, as indicated by the arrow A inFIG. 2, and to alternately close to prevent any substantial backflow ofblood through the valve in the upstream direction. The valve body 13defines a blood flow passageway in the form of its tabulated cylindricalinterior wall surface 17 which lies downstream of a curved entranceregion 19 at its upstream end, which is one of the important keys to theoverall valve design that has now been found to result in substantiallyincreased flow through the valve with low turbulence and substantiallyno generation of thrombosis. The details of the curved entrance region19 which extends axially for a distance not greater than about one-thirdof the average axial length of the valve body are discussed hereinafteralong with the operation of the valve. A pair of diametrically opposed,thickened wall sections 21, as best seen in FIG. 5, protrude inward froman otherwise right circular cylindrical surface, creating what isreferred to as a tabulated cylindrical surface as a result of thethickened sections 21 terminating in facing, parallel flat wall surfaces23 in which pairs of cavities or recesses 25 are formed that function asone-half of the pivot arrangement which controls the opening and closingmovements of the leaflets 15. Thus, the interior surface downstream ofthe curved entrance region 19 is generally rectilinear.

The valve body 13 preferably has a scalloped downstream profile so thatthere are, in effect, a pair of opposite shallow notches 27 formed inthe contour of the valve body 13 in the regions just downstream of thethickened wall sections 21. In a bileaflet valve of this type, thesenotches 27 provide side openings into the central passageway which arealigned with the central blood flow passageway in the region between theoutflow surfaces of the leaflets. Upon reversal of blood flow,backflowing blood will initially tend to laterally enter the valve bodypassageway through these side openings and will result in an initialupstream surge of blood into this central passageway region, creatingforces which impinge upon the outflow surfaces of the leaflets and,along with fluid drag forces acting on the leaflets 15, promote promptpivoting of the eccentrically mounted leaflets toward their closedposition orientations. This function is described in greater detail inU.S. Pat. No. 5,308,361, the disclosure of which is incorporated hereinby reference.

The exterior surface of the relatively thin valve body 13 in the regiondownstream of the flared entrance section 19 is substantially that of asurface of a right circular cylinder except for a slightly thickenedcentral portion wherein a shallow groove 29 is formed between a pair ofraised bands 29a. A metal stiffening attachment ring 30 of unique design(FIG. 2) which is formed with a plurality of circumferentially spacedapart inwardly protruding fingers 30a is mated therewith to addstability and rigidity to the valve body. The valve body itself ispreferably made of a suitable material, such as pyrocarbon orpyrocarbon-coated graphite, as is well known in this art, which hassufficient resiliency that it can be deformed so as to permit theinsertion of the pair of leaflets 15 in their operative locations. Themetal ring 30 is also used to support the sewing ring of appropriatedesign, as broadly known in this art. Detailed examples of sewing orsuture rings which can be employed are described in U.S. Pat. Nos.4,535,483 and 5,178,633, the disclosures of which are incorporatedherein by reference.

The thickened exterior bands 29a are strategically located in thedownstream cylindrical section of the valve body spaced from the flaredentrance section 19. As explained hereinafter in detail, the shallowgroove 29 is located to accommodate the inwardly protruding fingers 30aof the metal ring 30 in either orientation as explained hereinafter. Thegroove 29, which is of arcuate cross section and constitutes thenarrowest diameter on the exterior surface is located so that it iscompletely downstream of the fulcrums which are formed in recesses 25.This arrangement permits the suture rings to be accommodated in alocation where the remaining tissue annulus will be in contact with aportion of the right circular cylindrical exterior surface of the valvebody.

The leaflets 15 are preferably identical in form and shape and have tworectilinear, preferably flat, surfaces, i.e. an inflow surface 31 and anoutflow surface 33. The inflow surface is arbitrarily defined as thesurface which faces upstream when the leaflets are in the closedposition, whereas the outflow surface is the opposite downstream facingsurface. Each leaflet is preferably of substantially constant thicknesssuch that the surfaces 31 and 33 are parallel to each other. Otherleaflet configurations, such as sections of hollow cylinders of circularor elliptical cross-section may alternatively be employed, as discussedin more detail in U.S. Pat. No. 5,246,453, the disclosure of which isincorporated herein by reference.

Each leaflet 15 has a major arcuate downstream edge surface 35 which isshaped so as to abut and seat against the cylindrical side wall interiorsurface 17 of the valve body in the closed position. Each also has amating minor edge surface 37 which is located at the upstream edge inthe open position and which is preferably flat and formed at an angle soas to abut flush against the corresponding mating edge surface of theopposing leaflet in the closed position, as best seen in FIG. 4. Thecenterline plane is defined as a plane which includes the axialcenterline of the passageway which is perpendicular to the flat wallsurfaces 23. The pivot mechanism, as explained hereinafter, isconstructed such that the leaflets 15 can assume an orientationprecisely parallel to the centerline plane when blood is flowingdownstream through the valve body passageway.

The leaflets 15, as best seen in FIGS. 7-9, each have a pair ofintermediate straight edge surface regions 39 located between the minormating edge surface and the major arcuate edge surface which areinterrupted by a pair of laterally extending ears 41. The ears 41 havethe same thickness as the flat leaflets and are elongated in anupstream-downstream direction viewed in their open orientation. The earshave upstream lateral edge surfaces 43 and downstream lateral edgesurfaces 45 and are received in the cavities 25 in the flat wall regionsof the thickened interior wall sections. The flat lateral edge surfaces39 of the leaflets bear against the flat wall surfaces 23 surroundingthe cavities and act as bearing surfaces during the movement of theleaflets between the open and closed position, and short transitionsurfaces 47 interconnect the surfaces 35 and 39.

As previously mentioned, the valve body 13 is formed with the thickenedwall sections 21 in the regions where the cavities 25 are located, andpreferably these thickened sections are formed with flaring transitionsurfaces, i.e. an upstream transition surface 49 and a downstreamtransition surface 51 which lead smoothly from the circular entranceregion and the circular exit region of the valve body to the flat wallsurfaces 23 wherein the cavities 25 are located. A surface such as thesurface 49 may be referred to as a radial swept surface. As a result,the flow passageway through the valve body is generally circular incross-section except for the two thickened sections 21 which extendinward to the flat wall surfaces 23. As previously indicated, the planecontaining the centerline axis of the generally circular passageway thatis oriented perpendicular to the flat surfaces 23 is referred to as thecenterline plane and is frequently used for reference purposesthroughout this specification.

For a bileaflet valve such as that illustrated, the cavities 25 formedin the valve body are in the form of pairs of side-by-side cavitieswhich are mirror images of each other and which are respectively locatedon opposite sides of the centerline plane. As best seen in FIGS. 10 and10A, the cavities each have a generally flat rear wall 54 which issurrounded by an irregular side wall contour 53 that assists in guidingthe leaflets along the desired path in moving between the open andclosed positions. Generally, the cavities are formed to have an upstreamlobe 57 and a downstream lobe 59 on opposite sides of an intermediatethroat section 61. The intermediate throat section is formed by a pairof curved fulcrums, termed an outward fulcrum 63 and an inward fulcrum65 with respect to their location as reference to the centerline planeof the valve body. The upstream lobe 57 is formed with an inclined flatcamming wall 67 which extends upstream from a location above the outwardfulcrum 63 and joins a concavely curved wall section 69 which leadsgradually downstream from the junction point. The downstream lobe 59includes a flat wall section 71 immediately downstream of the inwardfulcrum 65, which serves as a stop against which the leaflet ears 41 canassume a precisely parallel orientation in the full open position, and adownstream sloping section 73 which extends from the downstream end ofthe flat wall section to the arcuate bottom wall 75 of the downstreamlobe.

The leaflets 15 are installed in the valve body 13 by squeezing the bodyat diametrically opposite locations so as to cause the flat wallsections 23 to spread sufficiently far apart to permit the leaflets tobe fitted into the valve body so that the ears are received in thecavities. The method and apparatus disclosed in U.S. Pat. No. 5,336,259,issued Aug. 9, 1994, can advantageously be used for the insertion of theleaflets. When the squeezing force is removed, the valve body 13 returnsto its original annular configuration leaving only the desired minimalclearance between the flat wall surfaces 23 of the valve body and thestraight lateral edge surfaces 39 of the leaflets. The metal stabilizingring 30 can be appropriately installed in the exterior circumferentialgroove 29 either following the installation of the leaflets or beforeinstalling the leaflets.

By designing the thickened bands 29a so that an inclined ramp is formedat the downstream edge of the downstream one of the two bands, it ispossible to install the metal ring 30 by sliding it upward from thedownstream end of the valve body 13 and allowing the fingers 30a to snapinto place; however, it should be understood that the ring could beinstalled by shrink-fitting if desired.

The unique stiffening ring 30 is designed to facilitate the installationof either an aortic sewing ring or a mitral sewing ring exterior of thevalve body 13, as best seen by comparing FIGS. 2 and 2A. In FIG. 2, anaortic sewing ring 81 is illustrated which is designed to leave theupstream exterior surface of the valve body free and clear to permit itsinsertion into the aortic annulus from which the defective natural valvewas excised. For this installation, the stiffening ring 30 is slid ontothe valve body 13 from the downstream end with the radially inwardprotruding fingers leading. As best seen in FIGS. 3 and 3A, thesefingers 30a are connected by relatively thin necks to the main portionof the stiffening ring, and the fingers have curved radially interiorfaces which are proportioned to the curvature of the grooves 29. Whenthe leading projection section reaches the downstream band 29a flankingthe groove 29, deflection of the fingers outward permits upstream travelto continue until the groove is reached, into which the projectingfingers then snap into place, as best seen in FIG. 15, with the mainportion of the stiffening ring tightly surrounding the downstreamcylindrical band 29a of the valve body and preferably placing it in atleast slight compression.

When the valve body is to be equipped with a mitral sewing ring 83 asdepicted in FIG. 2A, such sewing ring is positioned so as to occupy amajor portion of the exterior wall surface of the valve body 13 upstreamof the groove 29, leaving the downstream section free for insertion intothe tissue annulus from which the defective natural valve was excised.For this sewing ring, the stiffening ring 30 is installed with theopposite orientation, being slid upward from the downstream end of thevalve body 13 leading with the ring section 30 having the cylindricalradially interior surface. When it reaches the downstream band 29a, itis forced upstream therepast, and the metallic projecting fingers 30adeflect and slide over the downstream band 29a as before. The ringsection 30 bridges over the groove 29 onto the upstream band 29a, andsliding continues until the fingers 30a snap in place in the groove 29,at which time the ring is seated tightly about the upstream band 29a, asshown in FIGS. 2A and 13.

The depth of the shallow groove 29 is such that the thickness T₂ (FIG.14) at the location of the groove is equal to at least about 85% of thethickness T₁ of the major cylindrical section of the valve body. Thethickness T₃ at the location of the bands 29a need not be greater thanabout 120% of the thickness T₁. This strategic spacing and proportioningin a valve body 13 of the present design allows the wall thickness ofthe major portion of the valve body to be minimized, thus allowing alarger diameter opening for the passageway through the valve body.Generally, it is now felt that this interior diameter of the valveshould be as large as tolerable (while still providing adequatestructural strength) because the pressure loss through the valveincreases relative to the fourth power of the diameter. Of course, eachheart valve excised from the heart of a particular patient will varywith each patient, and therefore a surgeon should have available a setof prosthetic valves of different sizes generally ranging in exteriordiameter from about 19 millimeters to 33 millimeters in diameter forfully grown adults. The reference measurement is that of the tissueannulus remaining after the defective natural valve has been excised.

The present valve design is such that it can be effectively installed sothat the tissue annulus is in direct contact with the outer surface ofthe valve body 13 for valves that are installed both in the aorticposition and in the mitral position. In this respect, it should beunderstood that, when installed, the tissue annulus of the patient willbe in contact with the exterior surface of the valve body in the regionsmarked "A" in FIGS. 2 and 2A. One result of this arrangement is evidentfrom FIG. 2A where it can be seen that the diameter of the substantiallycircular passageway through the valve is a very large percentage of thediameter of the tissue annulus, which is made possible because of therelative thinness of the major portion of the valve body wall,particularly in the region of the tissue annulus.

Alternatively, as indicated above the ring can be heated and shrink-fitonto the valve body so that the main body of the ring 30 is in contactwith the desired band 29a. Such shrink-fitting allows greatercompressive force to be applied to a pyrocarbon structure by such ametal ring can improve the structural properties of the pyrocarbonwhich, as indicated above, is the preferred material of construction. Ofcourse, if the ring is to be installed prior to the installation of theleaflets, a metal is chosen which has sufficient resiliency to return toits perfectly annular shape following removal of the squeezing force.

With the heart valve 11 operatively installed in a patient in either themitral or the aortic position, when a pumping stroke of the heart causesdownstream flow of blood through the valve, the two leaflets 15 willassume an open equilibrium position with respect to instantaneous pathof the blood during conditions of high flow through the passageway. Thismay be an orientation where the leaflets 15 are aligned preciselyparallel to the centerline plane, as illustrated in FIG. 2. However,should the dynamic forces within the valve body passageway vary, theleaflets may pivot to some extent to accommodate such variance; forexample, the left-hand leaflet can rotate slightly clockwise to maintaina low energy position with respect to such an instantaneous change inthe direction of the blood flow.

As previously indicated, the combination of this particular support ofthe leaflets 15, together with the shape and proportioning of the valvebody 13 contributes to the achievement of smooth nonturbulent flow andthe absence of stasis. The toroidal curvature of the curved entrance end19 leading to a generally cylindrical valve body of substantial overallaxial length has been found to achieve this desired end. Morespecifically, the construction of a valve body to have a curved entrancetransition to a tabulated cylindrical, elongated passageway has beenfound to provide very low pressure drop for a passageway of a particulardiameter. The average axial length of the valve is preferably at least50% of the interior diameter thereof. The entrance section shouldconstitute not more than about one-third of the average axial length ofthe valve body, and it should smoothly join with the downstream section,preferably being tangent thereto. The entrance section is preferablyessentially a section of the surface of a torus. The torus is selectedso that the interior diameter of the torus is between 80% and 120% ofthe diameter of the interior circular cross-section of the passagewaythrough the valve body, and preferably between about 90% and 100%. Mostpreferably it is about 100% so that it will be substantially tangent tothe right circular cylindrical downstream interior surface; if not, ashort transition section is included. The radius of curvature of thecircle that is revolved to create the torus is between about 28% andabout 80% of the radius of the valve body and preferably between about40% and about 65%. In FIG. 14, the interior radius of the valve body ismarked "R₁ ", and the radius of curvature of the torus is marked "R₂ ".To facilitate aortic installation, the exterior diameter D_(E) at theentrance end 19 should not be more than about 10% greater than theexterior diameter D_(V) of the major cylindrical outer surface of thevalve body;

preferably, it is about 6-7% greater. By locating the stiffeningattachment ring at a location in the valve body that is downstream ofthe pivot axes of the leaflets, i.e. downstream of the fulcrums wherethe contact for pivoting is defined, it can accommodate suture ringsdesigned to have the tissue annulus directly lie in contact with theexterior surface of the valve body either upstream or downstream of suchsuture ring in the regions A in FIGS. 2 and 2A. Such an arrangementcontributes to a thinner wall thickness and a larger interior diameterfor the passageway.

Although at high rates of flow downstream through the valve, theleaflets can assume such precisely parallel alignment as describedhereinbefore, when the peak downstream flow of blood has passed and itis slowing to approach zero flow, the drag of the bloodstream againstthe leaflets 15 can cause the ears 41 to move slightly downstream in thedownstream lobes 59 which results in a pivoting of the leaflets a fewdegrees toward the closed orientation as shown in FIGS. 3 and 10A. Then,as the reverse flow of blood upstream through the valve begins, theleaflets immediately translate upstream, causing the ears to engage thecamming surfaces 67 of the contoured wall of the upstream lobe 57 abovethe outward fulcrums 63 which causes the leaflets to very promptly pivottoward their closed positions. This upstream translational movement ofthe ear 41 in the cavity 25 assures that the pivoting of each leaflettoward its closed position orientation occurs very promptly upon thebeginning of reverse flow and continues until the upstream edges of theleaflet ears reach the top of the upstream lobes 57. By this time, theleaflets 15 are oriented sufficiently transverse to the backflow ofblood that the force of the blood against the outflow surfaces 33becomes predominant, forcing the leaflets against the outward fulcrums63 and continuing the pivoting motion. The final movement of theleaflets to the closed position is guided by the movement of theupstream lateral edge surfaces 43 of the ears along the downstreamcurved portion 69 of the upstream lobes 57 while the ears remainessentially in contact with the outward fulcrums 63.

In the fully closed position, as illustrated in FIG. 4, the mating edges37 of the leaflets abut each other, and the downstream arcuate edgesurfaces 35 abut the cylindrical interior surface 17 of the valve body.In this fully closed position, the force of the blood against theoutflow surfaces 33 of the leaflets is borne by the seating of thearcuate edge surfaces 35 against the interior valve body wall 17 and bythe ears 41 bearing against the outward fulcrums 63 which also directsforces so that the two mating edges 37 are pressed together in sealingarrangement. The proportioning of the leaflets 15 within the valve body13 is such that some controlled leakage occurs in the cavities in anupstream direction past the ears. The dimensioning of the ears 41 andthe cavities 25 is such that this pathway for controlled backflow tendsto concentrate the leakage backflow in these regions where it achieves acleansing action that positively guards against the occurrence ofclotting at such locations. In this respect, the average clearancebetween the lateral edge surfaces of the ears and the rear walls 54 ofthe cavities is preferably at least about 50 microns to assure thedesired cleansing action.

When the blood flow again reverses, as for example when the pumpingstroke of the associated ventricle begins again, downstreamdisplacement, i.e. translation, of the leaflets 15 initially occurs as aresult of the force of the blood against the inflow surfaces 31. Theears 41 are guickly displaced so that they contact the inward fulcrums65 and create an eccentric pivot axis about which opening pivotingmotion guickly begins. Because of the shape of the downstream lobes,when blood flow reaches its maximum, the dynamic forces of thebloodstream in the passageway can cause the leaflets to assume aprecisely parallel position where the ears 41 are juxtaposed flushagainst the flat walls 71 just downstream from the inward fulcrums 65.

The overall design of the valve is such that gross hemodynamics in termsof energy loss per cardiac cycle are superior to mechanical heart valvesthat are presently commercially available. Because blood is a verydelicate tissue and even minor abuses caused by turbulence and highshear can result in thrombosis and emboli generation at local regions ofstagnation, this valve design which avoids the creation of excessiveturbulence and accompanying high shear stresses is particularlyadvantageous. Moreover, the design is such that the foregoing isaccomplished while also maintaining prompt closing which achievesreduced regurgitation without increased turbulence.

Although the invention has been described with respect to certainpreferred embodiments, which include what the inventors presentlyconsider to be the best mode for carrying out the invention, it shouldbe understood that various changes and modifications that would beobvious to one having the ordinary skill in this art may be made withoutdeparting from the scope of the invention which is defined by the claimsappended hereto. For example, as earlier indicated, two curvedrectilinear leaflets, three or more flat or curved leaflets, or even asingle occluder could be used instead of the two flat leaflets that areshown in the drawings.

Particular features of the invention are emphasized in the claims whichfollow.

What is claimed is:
 1. A prosthetic heart valve which comprisesagenerally tubular valve body having an interior sidewall which defines acentral passageway therethrough for blood flow in a downstreamdirection, said passageway having an axial centerline and beinggenerally circular in cross section except for a pair of diametricallyopposed flat interior sidewall surfaces, means surrounding said tubularvalve body for mounting said valve in association with a human heart,and at least two leaflets, each having a rectilinear inflow surface anda rectilinear outflow surface, said leaflets being mounted in said valvebody to open and close together to alternately permit flow of bloodtherethrough in a downstream direction when in an open orientation andto block the reverse flow of blood in an upstream direction when in aclosed orientation, said valve body and said leaflets beinginterconnected via a pivot arrangement by which said leaflets are guidedin movement between said open and closed orientations, said pivotarrangement being such that said rectilinear outflow and inflow surfacesassume an alignment substantially parallel to said valve passagewayaxial centerline when said leaflets are in a fully open orientation, andsuch that upstream translation thereof causes a positive pivotingmovement toward said closed orientation, said valve body having anupstream entrance end section formed with an interior surface that has aradius of curvature in a plane which contains said axial centerlinebetween about 28% and about 80% of said central passageway radius, whichentrance end connects to a downstream cylindrical section which has anaxial length greater than the axial length of said entrance end section,whereby downstream blood flow through said valve central passageway insaid open orientation is of a streamlined nature and pressure dropacross said heart valve is low.
 2. The prosthetic heart valve accordingto claim 1 wherein said upstream entrance end section comprises asection of a torus having an interior diameter generally equal tobetween about 80% and 120% of a diameter of said generally circularcentral passageway.
 3. The prosthetic heart valve according to claim 2wherein said upstream entrance end section comprises a section of atorus extending axially for a distance between about 10% and about 33%of an average axial length of said tubular valve body.
 4. The prostheticheart valve according to claim 1 wherein said valve body is axiallyelongated so that its average axial length is at least equal to about50% of a diameter of said generally circular central passageway.
 5. Theprosthetic heart valve according to claim 1 wherein said tubular valvebody is of substantially uniform wall thickness throughout except fortwo diametrically opposed interior surface regions wherein said flatinterior sidewall surfaces are located and except for exterior surfaceregions wherein attachment means is located for connection to said valvemounting means.
 6. The prosthetic heart valve according to claim 5wherein said valve body has a major exterior surface which is a surfaceof a right circular cylinder and lies downstream of said entrance endsection, wherein said attachment means includes a pair of thickenedbands which flank a groove for receiving a metal ring, wherein thediameter at the base of said groove is less than the diameter of saidright circular cylinder exterior surface, and wherein said surroundingmounting means includes a suture ring that is located axially of saidvalve body so that, when said valve is mounted in association with thehuman heart, an edge of a raw tissue annulus from which a defectivehuman valve was removed lies in direct contact with a section of saidmajor right circular cylindrical valve body exterior surface.
 7. Theprosthetic heart valve according to claim 1 comprising a bileaflet valvehaving exactly two leaflets wherein the downstream end of said valvebody is formed with a pair of diametrically opposed shallow notchesproviding lateral openings into the central portion of the valvepassageway, which lateral openings are aligned with said valve body flatinterior sidewall surfaces.
 8. A prosthetic heart valve which comprisesagenerally tubular valve body having an upstream end, a downstream endand an interior sidewall which defines a central passageway therethroughfor blood flow in a downstream direction, said passageway having anaxial centerline and being generally circular in cross section, meanssurrounding said tubular valve body for mounting said valve inassociation with a human heart, and at least one occluder having arectilinear inflow surface and a rectilinear outflow surface, saidoccluder being mounted in said valve body to open and close toalternately permit flow of blood therethrough in a downstream directionwhen in an open orientation and to block reverse flow of blood in anupstream direction when in a closed orientation, said valve body andsaid occluder being interconnected via a pivot arrangement by which saidoccluder is guided in movement between said open and closedorientations, said pivot arrangement being such that upstreamtranslation of said occluder causes its positive pivoting movementtoward said closed orientation, and said valve body having an upstreamentrance end section formed with an interior surface that has a radiusof curvature in a plane which contains said axial centerline betweenabout 28% and about 80% of said central passageway radius, whichentrance end section connects to a downstream cylindrical section whichhas an axial length greater than an axial length of said entrance endsection and which has a major cylindrical exterior surface of exteriordiameter D_(v) extending to said downstream end, and said upstreamentrance end section having an exterior diameter that is at least about6% greater than D_(v), whereby downstream blood flow through said valvecentral passageway in said open orientation is of a streamlined nature.9. The prosthetic heart valve according to claim 8 wherein said occluderhas rectilinear outflow and inflow surfaces and can assume an alignmentso that said surfaces are substantially parallel to said valvepassageway axial centerline when said occluder is in said openorientation.
 10. The prosthetic heart valve according to claim 8 whereinsaid at least one occluder comprises two leaflets, wherein said valvebody is formed with a pair of diametrically opposed flat interiorsidewall surfaces and wherein said downstream cylindrical section ofsaid valve body terminates in a pair of diametrically opposed shallownotches which provide openings laterally into a central portion of thevalve passageway, which lateral openings are aligned with said valvebody flat interior sidewall surfaces.
 11. The prosthetic heart valveaccording to claim 10 wherein said tubular valve body is ofsubstantially uniform wall thickness throughout except for twodiametrically opposed interior surface regions wherein said flatinterior sidewall surfaces are located and except for exterior surfaceregions wherein attachment means is located for connection to said valvemounting means.
 12. The prosthetic heart valve according to claim 8wherein said curved entrance section is essentially a section of a torushaving an interior diameter generally equal to between about 80% and120% of a diameter of said generally circular central passageway. 13.The prosthetic heart valve according to claim 8 wherein said upstreamentrance end section the comprises a section of a torus extends axiallyfor a distance between about 10% and about 33% of an average axiallength of said tubular valve body.
 14. The prosthetic heart valveaccording to claim 13 wherein said valve body is axially elongated sothat its average axial length is at least equal to about 50% of thediameter of said generally circular central passageway.
 15. Theprosthetic heart valve according to claim 13 wherein said torus has aninterior diameter equal to about a diameter of said generally circularcentral passageway and wherein said diameter of said entrance endsection is not more than about 10% greater than D_(v).
 16. Theprosthetic heart valve according to claim 8 wherein said valve body hasa major exterior surface which is a surface of a right circular cylinderand lies downstream of said entrance end section, wherein saidattachment means includes a pair of thickened bands in the sidewall ofsaid valve body which flank a groove for receiving a metal ring, whereina diameter at the base of said groove is less than a diameter of saidright circular cylinder exterior surface, and wherein said surroundingmounting means includes a suture ring that is located at an axiallocation along said valve body such that, when said valve is mounted inassociation with the human heart, an edge of a raw tissue annulus fromwhich the defective human valve was removed lies in direct contact witha section of said major right circular cylindrical valve body exteriorsurface.
 17. The prosthetic heart valve according to claim 16 whereinsaid valve body is axially elongated so that its average axial length isat least equal to about 50% of a diameter of said generally circularcentral passageway.
 18. The prosthetic heart valve according to claim 17wherein said groove is of arcuate cross section, wherein a thickness ofsaid valve body sidewall at said base of said groove is equal to atleast about 85% of a thickness T₁ of said major right circularcylindrical sidewall, and wherein said sidewall at said thickened bandshas a thickness which is not greater than about 120% of T₁.
 19. Aprosthetic heart valve for replacement of a defective aortic valvecomprisinga generally tubular valve body having an interior sidewallwhich defines a central passageway therethrough for blood flow in adownstream direction, said passageway having an axial centerline andbeing generally circular in cross section having a first radius, suturering means surrounding said tubular valve body for mounting said valvein association with a human heart, and occluder means having arectilinear inflow surface portion and a rectilinear outflow surfaceportion, which occluder means is mounted in said valve body to open andclose to alternately permit flow of blood therethrough in a downstreamdirection when in an open orientation and to block the reverse flow ofblood in an upstream direction when in a closed orientation, said valvebody and said occluder means being interconnected via a pivotarrangement by which said occluder means is guided in movement betweensaid open and closed orientations, said valve body having an upstreamentrance end section formed with an interior surface that has a radiusof curvature in a plane which contains said axial centerline betweenabout 28% and about 80% of said first radius, which entrance end sectionconnects to a downstream cylindrical section which has an axial lengthgreater than the axial length of said entrance end section, wherebydownstream blood flow through said valve central passageway in said openorientation is of a streamlined nature so pressure drop across saidheart valve is low, said entrance end section having an exteriorcircumferential surface that is concave and toroidal, and said suturering means being so located axially along the exterior surface of saidvalve body that a tissue annulus raw edge lies in direct contact withsaid concave toroidal exterior circumferential surface when said heartvalve is implanted in a patient.
 20. The prosthetic heart valveaccording to claim 19 wherein a major portion of said upstream entranceend section of said valve body is of substantially constant thicknessand wherein both said interior surface and said exterior surface thereofare in the form of at least 30% of a quadrant of a torus.